Definition
Mechanical devices on a retractable landing gear system that physically secure each gear leg in either the fully retracted (up) position or the fully extended (down) position. The uplock holds the gear up against the airflow and gravity after retraction, while the downlock holds the gear rigidly in place when extended so it can support the airplane's weight on landing.
Plain English
Latches that hold the landing gear firmly in place once it has finished moving — one set holds the gear up after takeoff, another set holds it down for landing.
Context Anchor
Seen during preflight inspection of airplanes with retractable landing gear, especially when checking the gear, doors, linkages, and visible locking parts for damage or security.
Why Pilots Care
If either mechanism fails, the gear may collapse on landing or fail to retract, creating an emergency and possible aircraft damage.
Analogy
Think of a folding chair that clicks into place when opened. The chair is not really safe to sit on until that locking part holds it firmly; landing gear also needs a positive lock in the position where it is meant to stay.
Intuition Check
“Lock” does not mean a key-operated lock here. It means a physical device that holds the landing gear in the up or down position so it does not move when it should stay fixed.
Example Sentence 1
During preflight, the pilot inspected the downlock mechanisms on each main gear leg for proper engagement and security.
Example Sentence 2
A faulty downlock mechanism allowed the gear to begin retracting while the airplane was still on the ground.